1. Field of the Invention
The present invention relates to a light emitting device having a plurality of light emitting elements and an optical apparatus using the light emitting device.
2. Description of the Related Art
In recent years, in the field of a light emitting device, a semiconductor laser (LD; laser diode) (hereinafter, referred to as a multi-wavelength laser) in which a plurality of light emitting sections, which emit light beams with different wavelengths, are formed on the same substrate (or the same base) has been actively developed. As an example of such a multi-wavelength laser, there is a laser in which a plurality of light emitting sections that emit light beams with different wavelengths are formed in one chip (so-called monolithic multi-wavelength laser). In this multi-wavelength laser, for example, a first laser oscillating section, which is formed by growing an AlGaAs-based semiconductor material by vapor deposition, and a second laser oscillating section, which is formed by growing an AlGaInP-based semiconductor material, are disposed in parallel at one surface side of a substrate, which is formed of GaAs (gallium arsenide), with a separation groove interposed therebetween. In this case, the oscillation wavelength of the first laser oscillating section is a 700 nm-band wavelength (for example, 780 nm), and the oscillation wavelength of the second laser oscillating section is a 600 nm-band wavelength (for example, 650 nm).
Moreover, for example, a laser in which a plurality of semiconductor lasers that emit light beams with different wavelengths are mounted in parallel on an arrangement base (so-called hybrid multi-wavelength laser) has also been proposed. However, the so-called monolithic laser described above is more effective in a point that the distance between light emitting points can be controlled with high precision.
These multi-wavelength lasers are used, for example, as laser light sources of optical disc apparatuses. Currently, in optical disc apparatuses, 700 nm-band semiconductor laser light is generally used for reproduction of a Compact Disc (CD) and used for recording and reproduction of recordable optical discs of a CD recordable (CD-R), a CD Rewritable (CD-RW), a Mini Disc (MD), and the like. In addition, 600 nm-band semiconductor laser light is used for recording and reproduction of a Digital Versatile Disc (DVD). Accordingly, by mounting the above-described multi-wavelength laser in an optical disc apparatus, recording or reproduction becomes also possible for a plurality of kinds of known optical discs. In addition, since the first and second laser oscillating sections are disposed in parallel on the same substrate (on the same arrangement base in a so-called hybrid semiconductor laser), only one package for a laser light source is made. Accordingly, since the number of components, such as an objective lens and a beam splitter for recording and reproduction of various kinds of optical discs, in an optical system can be reduced, the configuration of the optical system can be simplified. As a result, an optical disc apparatus can be made small at low cost.
In recent years, however, there has been a demand for higher density of an optical disc using a semiconductor laser which emits light with a shorter wavelength. As a constituent material of a semiconductor laser which meets such a demand, nitride-based Group III-V compound semiconductor (hereinafter, also referred to as GaN-based semiconductor) represented by GaN, an AlGaN mixed crystal and GaInN mixed crystal is known. A semiconductor laser using this GaN-based semiconductor can emit light with an oscillation wavelength of around 400 nm, which is a wavelength limit of an optical disc for which recording and reproduction are possible using a known optical system. Accordingly, it has been drawing much attention as a light source of a recording and reproduction apparatus for a next-generation optical disc. Moreover, it is also expected as a light source of a full-color display using three primary colors of RGB. For this reason, there is a demand for the development of a multi-wavelength laser including a GaN-based laser oscillating section.
As a known example of a multi-wavelength laser having a GaN-based laser oscillating section, a multi-wavelength laser has been proposed in which a first light emitting element having a GaN-based laser oscillating section and a monolithic second light emitting element, in which an AlGaAs-based first laser oscillating section and an AlGaInP-based second laser oscillating section are disposed in parallel at one surface side of a substrate, are laminated in this order on a support base (for example, refer to JP-A-2001-230502).